Automated movable welders are familiar to those who are skilled in the art, and therefore, a detailed discussion of these devices is neither warranted nor necessary for an understanding of the present invention. Such automated movable welders are described in several U.S. Pat. Nos. 6,178,819; 6,125,705; and 4,712,722, the teachings of which are all incorporated by reference. Nevertheless, for an understanding of the present invention, it should be appreciated that automated movable welders are operable to be attached to a given object which is to be welded. The automated welder then typically moves repeatedly along a prescribed path of travel to achieve a given welding objective.
For an automated welder to create a quality weld, it is important that the welding head borne by the welder be correctly positioned relative to the joint or seam between the two pieces of metal which are being welded. It is also important that this correct positional relationship be maintained as the automatic welder travels along the seam during the welding process.
During mechanized or automated welding, the prescribed path of the automated movable welder is typically guided by a track so that the welding head will follow a definite path along the seam or joint to be welded. Maintenance of the correct positional relationship between the welding head and the seam typically relies upon the precise positioning of the pieces to be welded, the correct positioning of the track on which the welder travels, and on the precise operation of the automated welder. Unfortunately, problems such as the imprecise positioning of the pieces to be welded, or incorrect positioning of the track, or malfunction in the operation of the automated welder may individually or in combination cause the welding head to be unsatisfactorily positioned relative to the seam with the result that the quality of the weld is diminished. Such unsatisfactory positioning of the welding head is commonly referred to as “mis-tracking”, and is highly undesirable.
Several devices to address the aforementioned problem, and which use optical and arc voltage sensing processes have been developed in an effort to provided more accurate tracking of the weld seam during on-going welding processes. In this regard, optical seam tracking methods typically use a laser to display a line or other pattern on the weld seam, ahead of the welding head. The resulting image, line, or pattern is then automatically interpreted by the welder to reveal the position of the weld seam. The automated welder then appropriately positions the welding head to more accurately track the weld seam.
Further, to the foregoing, arc voltage sensing systems are available and operate on the principal that the arc voltage will vary relative to the distance that the welding head is from the sidewall of the seam which is being welded. Therefore, by measuring the arc voltage during the welding process, the position of the welding head relative to the seam can be approximated, and the position of the welding head may then be appropriately adjusted to more accurately track the weld seam.
While these prior art devices and methods have operated with varying degrees of success, there have been shortcomings which have detracted from their usefulness. For example, in regards to the optical sensing processes, such as previously described, these systems must normally operate in the presence of a high level of ambient light which is emitted by the welding process, and which may fluctuate significantly over time. In this regard, when ambient light is reflected from the surrounding surfaces of the weld preparation it on occasion interferes with the interpretation of the image which is used by optical sensing process to reveal the correct position of the weld seam. Although these aforementioned problems associated with the ambient light may be alleviated, to some degree, through the use of highly specialized optical filters, such problems cannot be completely eliminated. Additionally, the welding process often produces smoke or fumes which may further distort or obscure relevant portions of the image. This of course, interferes with the interpretation of any resulting image.
Regarding the arc voltage sensing systems previously described, although such systems may be used to track weld seams formed by arc welding, such systems cannot be used to track weld seams formed by laser welding, electron beam welding, or other welding processes that do not use an arc. Additionally, the arc voltage sensing process does not work particularly well when the joint to be welded is nearly filled, and little sidewall remains to influence the arc voltage. Yet further, some arc welding processes, such as gas metal arc welding, inherently demonstrate significant fluctuations in arc voltage which may additionally interfere with accurate weld seam tracking.
In view of the foregoing, it would be highly desirable to provide a method and apparatus which facilitates accurate tracking of weld seams during the welding process, while substantially avoiding these and other perceived shortcomings of the prior art devices.